Electric field created in a bar by electrons deflected in a magnetic field

In summary, the conversation discusses a physics question from a sample AP Physics C E&M exam that involves analyzing a diagram to determine the direction of an electric field created by deflected electrons. The individual asking the question is stuck on parts e and f and is seeking clarification on how to solve the problem. They mention using the right hand rule and equations F = qE and F = qvB to solve for the electric field, but are unsure of the reasoning behind these solutions. The answer key provided states that the electric force balances the magnetic force, causing no net vertical force or movement.
  • #1
jdc15
40
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Hi everyone, first post here. Not sure if I'm posting in the right place but here goes. This question is from a sample AP Physics C E&M exam. It's kind of hard to explain without a diagram so I'll link to the exam:

Here is the link: http://apcentral.collegeboard.com/apc/public/repository/ap09_frq_physics_cem.pdf"
Answer Key: http://apcentral.collegeboard.com/apc/public/repository/ap09_physics_c_e_and_m_sgs.pdf"

Homework Statement


It's E&M #2 parts e and f. Starting with this: "The electrons moving through the bar are initially deflected by the external magnetic field. On the diagram below, indicate the direction of the additional electric field that is created in the bar by the deflected electrons." See the link. I understand up to part d but I'm stuck here.


Homework Equations


For part e, its more of a qualitative analysis using the right hand rule (I think). For part f, they use F = qE and F = qvB in the answer key but I'm not entirely sure why that is or how they get that solution.


The Attempt at a Solution


For part e, looking at the diagram, conventional current flows from a to b. Thus, electrons should flow from b to a. From the right hand rule, with the magnetic field running into the page, the force on the electrons should push them upwards. Thus, I get the electric field to be pointing downwards since electrons are negatively charged. However, the answer key says upwards. I have a feeling this has something to do with the electrons not actually causing the field or something like that.

For part f, well, I'm not quite sure where to begin. Why does the electric force balance the magnetic force as stated in the answer key?

It would be great if you could provide a link where I could read up on this.

Thanks in advance!
 
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  • #2
Never mind I figured it out. Since electrons are pushed to the top of the bar, the electric field pulls upwards. After they reach equilibrium, new flowing electrons will have to balance out the magnetic field and the electric field thus causing no net vertical force or movement (on average).
 

1. What is an electric field?

An electric field is a force field that surrounds electrically charged particles and causes them to either attract or repel each other.

2. How is an electric field created in a bar?

An electric field can be created in a bar by passing a current through it, as the movement of electrons creates an electric field.

3. What is the role of electrons in creating an electric field in a bar?

Electrons are negatively charged particles that can be deflected by a magnetic field, which causes them to move and create an electric field in the process.

4. How does a magnetic field affect the creation of an electric field in a bar?

A magnetic field can deflect the electrons in a bar, causing them to move and creating an electric field in the process.

5. What are some practical applications of understanding the electric field created in a bar by electrons deflected in a magnetic field?

Understanding this phenomenon can help in the design and function of devices such as electric motors, generators, and particle accelerators.

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